Frequently Asked Questions
1. The asbestos packing should be taken out to avoid electrochemical corrosion and damage to the valve stem. 2. Check the valve that has just entered the warehouse, and wipe clean the rainwater or dirt that enters during the transportation. The valve
passageway should be sealed with wax paper or plastic sheet, and then stored. 3. The processing surface of the valve that can rust in the atmosphere should be coated with anti-rust oil to protect it. 4.
For outdoor valves, protect the valve stem to prevent rain, snow, dust, and rust. It must be covered with rain-proof and dust-proof materials such as linoleum or tarpaulin. The warehouse where the valve
is stored must be kept clean and dry. 5. The thread of the valve stem often rubs against the nut of the valve stem. It is necessary to apply a little yellow dry oil, molybdenum disulfide or graphite powder
for lubrication. Turn the hand wheel regularly to add lubricant to the thread of the valve stem to prevent seizure. 6. For valves driven by actuators, lubricate the gearbox on time.
1. Acetic acid medium It is one of the most corrosive substances in organic acids. Ordinary steel will be severely corroded in acetic acid at all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. 316 stainless
steel containing molybdenum is also suitable for high temperature and dilute acetic acid vapor. . For harsh requirements such as high temperature and high concentration of acetic acid or containing other
corrosive media, high-alloy stainless steel or fluoroplastic valves can be selected. 2. Ammonia (Ammonia Hydroxide) Most metals and non-metals have slight corrosion in liquid ammonia and ammonia (ammonium
hydroxide), and only copper and copper alloys are not suitable for use. 3. Salt water (sea water) The corrosion rate of ordinary steel in sodium chloride solution, sea water and salt water is not very high,
and coating protection is generally required. Various types of stainless steel also have a very low uniform corrosion rate, but may cause localized corrosion due to chloride ions, usually 316 stainless steel
is better. 4. Alkali (sodium hydroxide) Steel is widely used in sodium hydroxide solution below 80°C and 30% concentration. There are also many petrochemical plants that still use ordinary steel when the
temperature is below 100°C and 75%. Although corrosion increases, it is economical. 5. Alcohols, ketones, esters, ethers Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc., ketone
media include acetone, butanone, etc., ester media include various methyl and ethyl esters, and ether media include methyl ether, ethyl ether, etc. Butyl ether, etc., they are basically non-corrosive, and
common materials can be applied. When selecting, a reasonable choice should be made according to the properties of the medium and related requirements. It is also worth noting that ketones, esters, and ethers
are soluble in a variety of rubbers. Avoid mistakes when choosing sealing materials.
Advantages: 1. The fluid resistance is small. 2. Simple structure, relatively small size, light weight and easy maintenance 3. Good sealing performance. 4. It is not restricted by the installation direction, and the flow direction of the medium can be
arbitrary. 5. No vibration and low noise. Disadvantage: Ball valves can be divided into floating ball valves, fixed ball valves, elastic ball valves and oil-sealed ball valves according to their structure.
According to the channel, it can be divided into direct energy type, angle type and three-way type. The three-way type can be divided into T-shaped and L-shaped. According to the connection method, it can
be divided into three types: threaded connection, flange connection and welding type. The following matters should be paid attention to when installing and maintaining the ball valve:. 1. Leave a position
for the valve handle to rotate. . 2. Cannot be used for throttling. 3. The ball valve with drive mechanism should be installed upright.
Since the valve was produced to the present, its sealing technology has also undergone great development. So far, valve sealing technology is mainly embodied in two aspects, namely static sealing and dynamic sealing. The so-called static seal usually
refers to the seal between two static surfaces. The sealing method of static seal mainly uses gaskets. The so-called dynamic sealing mainly refers to the sealing of the valve stem, that is, preventing the
medium in the valve from leaking with the movement of the valve stem. The sealing method of dynamic sealing is mainly to use a stuffing box.
1. The fault occurs at each connection. Cryogenic valves belong to this type of failure, such as valve packing running and freezing, valve seat and pipeline connecting flange leakage, valve screw sleeve at both ends of the tin filling thread leakage and
so on. The valve stem packing is generally in the packing groove where the valve stem is close to the wall of the cold box. When the packing is uneven or not tight, or the valve stem is not straight or round,
cryogenic liquid or gas will leak out along the gap in the packing. Due to the external cold transfer, the moisture in the air will freeze on the packing, freezing the valve stem. In this case, only use
steam or hot water to heat the filler to open and close the valve. However, after the valve is opened and closed, the water accumulated in the packing will freeze again. Because the valve switch is laborious,
the fire valve often causes the valve stem to twist and the hand wheel to break. Therefore, after the valve is overhauled, the packing should be evenly packed and tightened, and the compression nut should
be tightened. During the overall leak test of the air separation plant, the leakage at the lower valve stem packing should also be checked, and this problem should be solved before the cold start. The common
causes of flange leakage are unsmooth and uneven sealing surface, insufficient pipeline compensation, uneven bolt tightening, improper bolt material, etc. Both ends of the outer threaded sleeve of the valve
stem are connected with tin-filled threads, which are prone to cracks and leakage after long-term use. When pressure test leaks, if such a leak is found, It is best to pull out the valve stem and refill
it with tin and tighten it, and it is best to use silver welding. Cryogenic valve is an equipment that should be maintained frequently during the normal operation of air separation equipment. We should have
high standards, strict requirements, careful maintenance and good use. 2. The fault occurred on the top of the valve. The valve top (valve head) of this kind of valve is movably connected with the valve
stem, so that the two sealing surfaces can be "automatically aligned" when the valve is closed. After long-term use, titanium, nickel, zirconium, Monel and alloy valves are sometimes damaged by the anti-return
gasket, which causes the locking nut to loosen, and finally the valve top falls off when the valve is opened. At this time, the valve will lose its closing function. Sometimes the damage of the lock nut
is caused by improper material, replaced by cold brittle metal. Another common fault is that the valve top is not tightly closed, that is, the valve is leaking. The common reason is that the valve top and
the sealing surface of the valve seat are crushed by hard objects (such as silica gel, metal shavings, welding slag and other hard objects), forming dents. In this case, the marine valve often uses a lot
of effort to close the valve, and the result is that the pressure injury is aggravated. Sometimes the valve stem center line is not perpendicular to the valve seat sealing surface (valve surface), or the
valve top and valve surface are worn out due to long-term use, which will cause the valve to leak. 3. The failure occurred on the valve stem. The more common fault is the wear of the thread on the valve
stem and screw sleeve, and the ceramic valve [door makes the valve unable to close. Generally, the threaded thread of the valve stem is not easy to wear out, and the female thread on the screw sleeve (brass)
is easy to be damaged. The reason is mostly because the valve is opened with too much force, or it is still twisted hard after it is opened or closed, causing the thread to bite. Sometimes the thread is
completely "bitten" and the valve can only be opened but not closed. To close the valve, you can only use a temporary bolt to push the valve stem inward and wait for maintenance before repairing. To prevent
this kind of failure, the most important thing is not to use too much force when opening and closing the valve, and do not open or close hard when opening or closing the valve.